1. Field of the Invention
The present invention relates to an electronic mail system for efficiently transmitting mail data coping with the fluctuation of the transmission quality of each wireless transmission path, which is a constituent of the communication network for connecting the mail server and clients.
2. Description of the Related Art
Most conventional electronic mail systems (abbreviated as xe2x80x9ce-mail systemsxe2x80x9d, hereinbelow) have been developed on the premise of using a wire communication line as the transmission path. In wire communication lines, transmission quality is stable and thus it is unnecessary to consider problems such as fluctuation of the transmission quality or disconnection of the line during the mail data transmitting or receiving operation. Such a problem often occurs in the wireless-line communication. In an example method of efficiently operating the e-mail system, priority is set for each e-mail (i.e., electronic mail) in accordance with the importance or urgency of the e-mail so as to rearrange the e-mail data, where such a rearranging operation is executed after the current e-mail is received by the relevant client. Examples of the above kind of conventional e-mail system are disclosed in Japanese Unexamined Patent Application, First Publication, Nos. Hei 4-82347 and Hei 5-22339.
However, recently, data transmission using mobile terminals such as cellular phones has been widespread, and data transmitting or receiving operation is often performed under an undesirable condition, that is, with degraded transmission quality generated when the mobile terminal moves with a high speed or when a weak radio wave is received. When an e-mail is sent using such a degraded communication line, retransmission may be necessary, and as the number of repeating retransmission increases, a longer transmission time is necessary.
If a plurality of mail data addressed to a client are stored in a mail server, the mail data are sent to the client in turn according to the order of arrival of the mail data when a mail data sending request is sent from the client. Therefore, when a relatively large mail data is stored at the head (top of the output queue) and relatively small mail data is stored after the relatively large mail data, if the wireless transmission path becomes unstable, then the relatively large mail data is not stably transmitted and thus the following relatively small mail data may not be transmitted, so that the number of normally received mail data decreases.
In general data communication, the calling and called sides use a protocol defined for correctly sending data, in which data is divided into data units, each having a specific data amount, and it is confirmed whether each data unit has been normally sent and received, and if the confirmation fails, the relevant data unit is retransmitted. According to such a protocol, divided data units of mail data are sent in turn, and when all data units of an e-mail have been sent and received, the mail-data transmitting operation is completed. Therefore, the probability of completion of the mail-data transmission decreases in inverse proportion to the size of the mail data. As the size of the mail data increases, the number of data units, each having a specific data amount, increases; therefore, the number of times for confirming whether the data is normally sent and received increases and the probability of retransmission of each divided data unit also increases. Accordingly, the transmission time of data corresponding to an e-mail becomes longer, and a longer time is necessary for completing the mail data transmission if the transmission condition of the wireless transmission path is unstable.
As described above, in the conventional e-mail system, a plurality of mail data stored in the mail server are sent to a relevant client in their arrival order. Therefore, if the wireless transmission path is unstable and relatively large mail data is sent first, the transmission of the relatively large mail data takes a long time, and the following small mail data may not be sent, thereby degrading the mail data transmission efficiency. In addition, in the conventional system, the mail data sent while the wireless transmission path is stable is not always relatively important and urgent mail data; therefore, efficient transmission according to a user""s request, such as sending an important e-mail first, cannot be performed.
In consideration of the above circumstances, an objective of the present invention is to provide an electronic mail system for monitoring the condition of receiving mail data so as to cope with a change of the condition of a wireless transmission path in the communication network, and for efficiently transmitting mail data when the transmission quality is degraded, by, for example, rearranging the order of sending mail data stored in the mail server and sending an e-mail having a smaller data size first.
Therefore, the present invention provides an electronic mail system comprising:
a mail server having a mail sender which is connected to a first communication network including a data communication network and which receives an electronic mail and sends the received electronic mail to a relevant client;
a client having a mail receiver for receiving the electronic mail sent from the mail sender; and
a second communication network including a wireless transmission path, for connecting the mail server and the client, wherein:
the mail sender comprises:
a first mail receiving unit for receiving mail data of each electronic mail sent via the first communication network,
a storage device for storing the mail data received by the first mail receiving unit in turn;
a mail sending unit for reading out the mail data stored in the storage device, and sending the readout data to the second communication network;
a command interpreting section for receiving and interpreting a command, generated by the client, sent via the second communication network, and outputting a signal ordering rearranging the mail data stored in the storage device; and
a mail order rearranging section for rearranging the order of the mail data stored in the storage device, based on the signal sent from the command interpreting section, and
the mail receiver comprises:
a second mail receiving unit for receiving a wireless signal from the second communication network, and demodulating and storing the mail data from the received signal, and monitoring the condition of receiving the wireless signal of the mail data so as to detect a change of the receiving condition and output a detection signal;
a receiving condition monitoring section for receiving the detection signal indicating a change of the receiving condition from the second mail receiving unit, and outputting a signal ordering the issue of a command; and
a command issuing section for sending a command signal according to the output from the receiving condition monitoring section to the second communication network.
In the above basic structure, the second mail receiving unit may comprise a radio wave monitoring section for detecting and outputting the intensity of the received radio wave of the wireless signal at predetermined intervals, and generate the detection signal indicating a change of the receiving condition based on the output from the radio wave monitoring section.
In this case, it is possible that the output from the radio wave monitoring section is compared with a predetermined threshold value, and the detection signal is generated when the intensity of the received radio wave becomes lower than the threshold value.
It is also possible that a variation of the intensity of the received radio wave per unit time is calculated based on the output from the radio wave monitoring section, and the detection signal is generated when the variation becomes larger than a predetermined threshold value.
Also in the above basic structure, the mail data may be sent to the mail receiving unit in a divided form; and the second mail receiving unit may comprise a mail receiving section for reconstructing and outputting the mail data corresponding to an electronic mail, and also outputting information on the size of the reconstructed mail data at predetermined intervals. In this case, it is possible that the second mail receiving unit calculates the speed of reconstruction of the mail data at predetermined intervals based on the data size information output from the mail receiving section, and generates the detection signal indicating a change of the receiving condition based on the calculated speed of reconstruction.
In the above case, the second mail receiving unit may compare the speed of mail data reconstruction with a predetermined threshold value, and generate the detection signal when the speed becomes lower than a predetermined threshold value.
Also in the above case, the second mail receiving unit may calculate a variation of the speed of mail data reconstruction per unit time, and generate the detection signal when the variation becomes larger than a predetermined threshold value.
In a preferable example, the second mail receiving unit comprises a storage device for storing the received mail data and outputting information on the vacant capacity at predetermined intervals, and generates the detection signal indicating a change of the receiving condition when the vacant capacity of the storage device, detected according to the information on the vacant capacity, becomes lower than a predetermined capacity.
In another preferable example, the second mail receiving unit comprises an input device for a user of the mail receiver to input a signal for communicating a change of the receiving condition, or a signal for ordering the rearrangement of the sending order of mail data stored in the mail sender; and the second mail receiving unit generates the detecting signal supplied to the receiving condition monitoring section, based on a signal input via the input device.
It is also possible that:
the second mail receiving unit comprises a wireless data processing section for receiving and demodulating the wireless signal from the second communication network, and measuring an error rate of the demodulated digital signal of the mail data according to specific codes included in the digital signal; and
the second mail receiving unit generates the detection signal when the measured error rate of the digital signal becomes larger than a predetermined threshold value.
It is also possible that the second mail receiving unit comprises a radio wave monitoring section for measuring the power supply voltage of the mail receiver at predetermined intervals, and generates the detection signal when the measured power supply voltage becomes lower than a predetermined threshold value.
According to the present invention, the condition of receiving mail data is monitored by the mail receiver at the client side so as to detect a change of the transmission condition of the wireless transmission path. When a change is detected, a command is sent to the mail server side so that the sending order of the mail data can be rearranged. Therefore, it is possible to efficiently transmit the mail data under the degraded transmission quality, thereby improving the operation efficiency of the electronic mail system.
In the rearrangement of the mail data performed by the mail order rearranging section, the order of the mail data may be determined according to the degree of importance or urgency of each electronic mail.
Typically, the storage device in the mail sender also stores mail data storage information which indicates a property of each electronic mail.
Accordingly, the priority of the transmission can be set for each e-mail (i.e., electronic mail) in accordance with the importance or urgency of the e-mail so as to rearrange the e-mail data, thereby improving the convenience of the e-mail system.